This proposal is in response to a Request for Applications concerning "Diagnostic Centers for Psychiatric Linkage Studies". The overall goal of this proposal is to identify sib-pairs with Alzheimer's disease (AD), i.e., patients with AD who have siblings with symptoms of AD. It is also hoped that many of these cases will have informative family histories in relation to AD, i.e., evidence of dementia in parents and multiple other ancestors. The diagnosis of AD in the index cases will be established by contemporary research criteria. Blood samples will be obtained from sib pairs and all living individuals in large families with AD. Blood will be used for the preparation of genomic DNA and establishment of permanent lymphoblastoid cell lines at the NIMH. Although the final assessment procedures will be decided collaboratively, this proposal presents the methods that seem optimal at the present time for carrying out these activities. This application for a Diagnostic Center for Psychiatric Linkage Studies is one of three submissions from the Joint Departments of Psychiatry at Harvard Medical School. Each application focuses on a different disorder and is intended to be evaluated independently of the other two. However, if funded, these three proposals will be implemented in a coordinated fashion and, where applicable, consistency of methodology across sites will be maintained.